0 = -1(x-2)(x+4) is not equivalent to 0 = -1(x+2)(x-4)
You have:
0 = -1(x-2)(x+4)
which means that
0 = (x-2)(x+4)
Multiplying by -1 at both sides:
(-1)*0 = (-1)*(x-2)(x+4)
0 = (-x + 2)(x + 4)
Multiplying by -1 at both sides again:
(-1)*0 = (-x + 2)(x + 4)*(-1)
0 = (-x + 2)(-x - 4)
Multiplying by -1 at both sides again:
(-1)*0 = (-1)*(-x + 2)(-x - 4)
0 = -1(-x + 2)(-x - 4)
which is different from
0 = -1(x+2)(x-4)
